Messages in this thread | | | Date | Tue, 6 Oct 2015 11:07:34 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() |
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On Tue, Oct 06, 2015 at 10:43:11AM -0700, Josh Triplett wrote: > On Tue, Oct 06, 2015 at 10:36:46AM -0700, Paul E. McKenney wrote: > > On Tue, Oct 06, 2015 at 10:18:39AM -0700, Josh Triplett wrote: > > > On Tue, Oct 06, 2015 at 09:13:42AM -0700, Paul E. McKenney wrote: > > > > Currently, __srcu_read_lock() cannot be invoked from restricted > > > > environments because it contains calls to preempt_disable() and > > > > preempt_enable(), both of which can invoke lockdep, which is a bad > > > > idea in some restricted execution modes. This commit therefore moves > > > > the preempt_disable() and preempt_enable() from __srcu_read_lock() > > > > to srcu_read_lock(). It also inserts the preempt_disable() and > > > > preempt_enable() around the call to __srcu_read_lock() in do_exit(). > > > > > > What restricted environments do you intend to invoke > > > __srcu_read_lock from? > > > > > > This change seems fine, but I don't see any change in this patch series > > > that needs this, hence my curiosity. > > > > Someone asked me for it, and now I cannot find it. :-( > > > > Something to the effect of when running unmapped during exception entry > > or something like that. I guess one way to find out would be to remove > > the commit and see who complained, but on the other hand, it arguably > > makes more sense to have only the bare mechanism is __srcu_read_lock() > > and put the environmental protection into srcu_read_lock(). > > I agree; I just find the idea that someone would need to call > __srcu_read_lock rather than srcu_read_lock odd and worthy of further > understanding. :)
And they did supply an explanation that seemed satisfactory at the time, but I cannot find that either. I clearly need to track that sort of stuff better!
Thanx, Paul
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